On 03/25/2017 06:43 PM, Viktor Dukhovni wrote:
On Mar 25, 2017, at 9:05 PM, Doug Barton <domain_name_t...@yahoo.com> wrote:
Postfix can be configured to try IPv6 before IPv4 (with
smtp_address_preference)
Regarding that option, I've never understood the warning in postconf(5).
Doesn't that feature provide precedence, not exclusivity? Or put a different
way, if the site cannot be reached by IPv6, won't postfix retry with IPv4?
See
http://www.postfix.org/postconf.5.html#inet_protocols
http://www.postfix.org/postconf.5.html#smtp_address_preference
If IPv6 is explicitly preferred, rather than randomly selected as with:
smtp_address_preference = any
then an MX host with sufficiently many IPv6 addresses will never be
tried over IPv4 because the number of connection attempts and SMTP
sessions are limited:
http://www.postfix.org/postconf.5.html#smtp_mx_address_limit
http://www.postfix.org/postconf.5.html#smtp_mx_session_limit
One or the other might be exceeded before any IPv4 addresses are
tried.
That makes sense, thanks. It might be nice to have that information, or
a pointer to it, included in postconf(5).
Doug
